24 versus 48 volt and panel array size

[Chewbacca]

T-105 batteries

Perhaps, but are you putting six strings of four of those batteries each in parallel? In addition the OP did not have enough solar to properly keep them charged.

N

My setup is actually much worse than that. I have 4 strings of 6v golf cart batteries (costco) and 1 string NAPA 7266 commercial 12 v. (craigslist) running in parallel. Charged off 6 Sharp 240v panels 3 on east roof face and 3 on west. When new the batteries would last until 5 am now they are done at 9 pm. (part of the problem is the trees are bigger in my yard now) Running 6000 btu ac off 1500 watt power2go inverter and morningstar charge controller . Sole purpose of the solar panels is to cool the house exc in winter I run the kitchen/den circuit off it. Back to the OP I would say it depends how much he draws the batteries down. If he goes to work and turns out the lights, he should have 28-30 volts waiting for him at 6:00pm when he gets home. That should take care of the sulfate issue. No? I am by no means an expert.

[lkruper]

N

My setup is actually much worse than that. I have 4 strings of 6v golf cart batteries (costco) and 1 string NAPA 7266 commercial 12 v. (craigslist) running in parallel. Charged off 6 Sharp 240v panels 3 on east roof face and 3 on west. When new the batteries would last until 5 am now they are done at 9 pm. (part of the problem is the trees are bigger in my yard now) Running 6000 btu ac off 1500 watt power2go inverter and morningstar charge controller . Sole purpose of the solar panels is to cool the house exc in winter I run the kitchen/den circuit off it. Back to the OP I would say it depends how much he draws the batteries down. If he goes to work and turns out the lights, he should have 28-30 volts waiting for him at 6:00pm when he gets home. That should take care of the sulfate issue. No? I am by no means an expert.

How many cycles at what % DOD have you gotten so far from your Costco batteries?

[Chewbacca]

Charge

How many cycles at what % DOD have you gotten so far from your Costco batteries?

I am using the default acid/lead charging program on the Morningstar charge controller. The Power2go inverter allows drawdown to 19.1v under load before shutting off which happens daily so doing the math 365 X 5yrs = 1825 cycles. The batteries usually have about 23 volts by 6 am. At 2:40 pm with all six panel in full sun I am showing 27.1 volts with the 6k btu ac pulling a load.

[lkruper]

I am using the default acid/lead charging program on the Morningstar charge controller. The Power2go inverter allows drawdown to 19.1v under load before shutting off which happens daily so doing the math 365 X 5yrs = 1825 cycles. The batteries usually have about 23 volts by 6 am. At 2:40 pm with all six panel in full sun I am showing 27.1 volts with the 6k btu ac pulling a load.

If you have the Interstate Costco batteries they are selling now, their customer service told me that they get 1220 cycles at 50% DOD and 650 cycles at 80% DOD. If I understand you correctly, you allow a 24v battery bank to get down to 19.1v, which is 1.6v per cell which is to drain them 100% every day for 5 years.

If I could ask for clarification, these are the same batteries you have had in continuous service for 5 years, draining to 0% SOC on a daily basis?

[Chewbacca]

If you have the Interstate Costco batteries they are selling now, their customer service told me that they get 1220 cycles at 50% DOD and 650 cycles at 80% DOD. If I understand you correctly, you allow a 24v battery bank to get down to 19.1v, which is 1.6v per cell which is to drain them 100% every day for 5 years.

If I could ask for clarification, these are the same batteries you have had in continuous service for 5 years, draining to 0% SOC on a daily basis?

Not exactly correct, but I was over-simplifying a rather disjointed process. I started with two banks of 4x6v and about 6 months later added another bank (because I could tell I was wasting a lot of sunlight) and a year later added another bank of costco batteries so I have had 4 banks of 4 six volt batteries since 2012. Then added the two used NAPA 12 volt batteries in 2013. Replaced one of those with a new one in 2014. Sometimes the solar doesn't get plugged in or vacations happen so we can subtract 200 from my original number of cycles (for the original two banks) and be a little more correct. When the inverter quits it is under load, so voltage jumps back to 21-22v pretty quickly afterwards, so whatever SOC that is. I just bought a hydrometer today, just need to learn how to use it now... You are starting to scare me... I have Zombie batteries!!

[lkruper]

Not exactly correct, but I was over-simplifying a rather disjointed process. I started with two banks of 4x6v and about 6 months later added another bank (because I could tell I was wasting a lot of sunlight) and a year later added another bank of costco batteries so I have had 4 banks of 4 six volt batteries since 2012. Then added the two used NAPA 12 volt batteries in 2013. Replaced one of those with a new one in 2014. Sometimes the solar doesn't get plugged in or vacations happen so we can subtract 200 from my original number of cycles (for the original two banks) and be a little more correct. When the inverter quits it is under load, so voltage jumps back to 21-22v pretty quickly afterwards, so whatever SOC that is. I just bought a hydrometer today, just need to learn how to use it now... You are starting to scare me... I have Zombie batteries!!

So, my furry friend, how many cycles have you gotten from the Costco batteries at 100% DOD? Would that be every day for three years minus about 100? That's about 1000 cycles, and from what I have been told by the manufacturer (assuming you have Interstate Batteries from Costco) you should not expect more than 650 cycles at 80% DOD. However, that does not mean the batteries suddenly stop working. Batteries are considered time to replace when they reach about 80% of original capacity and then they will go downhill faster after that.

You may not know how your batteries are performing relative to new as you have quite a mixture of kinds of batteries as well as old and new together. I have been told that adding new batteries to old batteries also drags down the new ones to the level of the old ones.

Its good to get a hydrometer, BTW.

[Chewbacca]

80%

So, my furry friend, how many cycles have you gotten from the Costco batteries at 100% DOD? Would that be every day for three years minus about 100? That's about 1000 cycles, and from what I have been told by the manufacturer (assuming you have Interstate Batteries from Costco) you should not expect more than 650 cycles at 80% DOD. However, that does not mean the batteries suddenly stop working. Batteries are considered time to replace when they reach about 80% of original capacity and then they will go downhill faster after that.

You may not know how your batteries are performing relative to new as you have quite a mixture of kinds of batteries as well as old and new together. I have been told that adding new batteries to old batteries also drags down the new ones to the level of the old ones.

Its good to get a hydrometer, BTW.

I agree that some of my batteries are 80% or less now, but I am not ready to cough up $1,488 for 9 extra hours of battery power. Solar is still saving me about $50 a month in air-conditioning grid charges. And yes mixing batteries is a bad thing, but they were cheap and big! I took the risk. The point is why buy the expensive trojan 2 volt battery? If they last 10 years they still aren't cost-effective over a 5 year Costco one. Batteries are a stupid way to store power anyways cost wise. It takes a huge number of them to power a typical house and then 5 or 7 years later you start over, and have to buy new ones. Not to mention the frickin maintenance! Now that this experiment has taught me, my future (dream) setup will use water pumped to a water tower or pond via solar panels to store energy and use a hydro generator to keep a relatively small battery bank at a constant voltage state. I haven't finished doing the math on that one though. How many gallons at what height produces... So, anyways if all I can power with virtually the same setup as the OP is a small ac unit. How is he going to power an entire house?

[lkruper]

I agree that some of my batteries are 80% or less now, but I am not ready to cough up $1,488 for 9 extra hours of battery power. Solar is still saving me about $50 a month in air-conditioning grid charges. And yes mixing batteries is a bad thing, but they were cheap and big! I took the risk. The point is why buy the expensive trojan 2 volt battery? If they last 10 years they still aren't cost-effective over a 5 year Costco one. Batteries are a stupid way to store power anyways cost wise. It takes a huge number of them to power a typical house and then 5 or 7 years later you start over, and have to buy new ones. Not to mention the frickin maintenance! Now that this experiment has taught me, my future (dream) setup will use water pumped to a water tower or pond via solar panels to store energy and use a hydro generator to keep a relatively small battery bank at a constant voltage state. I haven't finished doing the math on that one though. How many gallons at what height produces... So, anyways if all I can power with virtually the same setup as the OP is a small ac unit. How is he going to power an entire house?

I recently did a comparison of batteries on this forum compared to Costco and at $83.99 for a 6v 207AH battery that is said by Interstate to get 1220 cycles at 50% DOD, I came to the conclusion that they are the lowest cost in cents / kWh. That being said, their 1220 cycles may be a bit optimistic.

[Chewbacca]

I recently did a comparison of batteries on this forum compared to Costco and at $83.99 for a 6v 207AH battery that is said by Interstate to get 1220 cycles at 50% DOD, I came to the conclusion that they are the lowest cost in cents / kWh. That being said, their 1220 cycles may be a bit optimistic.

I was hoping someone on this forum had experience with the Trojan 2v battery they could impart.

[inetdog]

I was hoping someone on this forum had experience with the Trojan 2v battery they could impart.

The Trojan 2V is a pretty specialized battery, so there are not going to be too many forum members who have used it or even evaluated it in depth.
Your best bet would probably be Sunking (Dereck) if he is around at the moment.

Some large 2V batteries are actually several independent cells, with their own electrolyte reservoirs (check SG and level through each of the caps), that are paralleled by internal interconnecting bars rather than wired in series.
Except for being identical at the start and being thermally linked and electrically connected with very low series resistance, I would expect those batteries would be subject to some of the disadvantages of paralleled batteries.

[lkruper]

I was hoping someone on this forum had experience with the Trojan 2v battery they could impart.

Not me, you have more real experience than I do

[lkruper]

I agree that some of my batteries are 80% or less now, but I am not ready to cough up $1,488 for 9 extra hours of battery power. Solar is still saving me about $50 a month in air-conditioning grid charges. And yes mixing batteries is a bad thing, but they were cheap and big! I took the risk. The point is why buy the expensive trojan 2 volt battery? If they last 10 years they still aren't cost-effective over a 5 year Costco one. Batteries are a stupid way to store power anyways cost wise. It takes a huge number of them to power a typical house and then 5 or 7 years later you start over, and have to buy new ones. Not to mention the frickin maintenance! Now that this experiment has taught me, my future (dream) setup will use water pumped to a water tower or pond via solar panels to store energy and use a hydro generator to keep a relatively small battery bank at a constant voltage state. I haven't finished doing the math on that one though. How many gallons at what height produces... So, anyways if all I can power with virtually the same setup as the OP is a small ac unit. How is he going to power an entire house?

If we ignore your two 12v batteries, I count 16 6v batteries. At Costco's price that would be $1344 or $1584 with core. At $50 savings per month, that would be 27 months to break even just on the cost of the batteries, if core is not considered. So, if you have gotten 3+ years out of them so far at 100% DOD you have done pretty well. Have you done any calculations as to your total cost in terms of cents / kWh for your solar system?

[SunEagle]

If we ignore your two 12v batteries, I count 16 6v batteries. At Costco's price that would be $1344 or $1584 with core. At $50 savings per month, that would be 27 months to break even just on the cost of the batteries, if core is not considered. So, if you have gotten 3+ years out of them so far at 100% DOD you have done pretty well. Have you done any calculations as to your total cost in terms of cents / kWh for your solar system?

I suspect that some of that $50 savings comes from energy generated directly from the panels during the mid day and not just the batteries. I seriously doubt the batteries (even at the low Costco price) will pay for themselves in the 3+ years owned.

Also since the battery system kept being bolstered by new ones over a period of months it might be hard to get a true cost/kWh on any of them.

[lkruper]

I suspect that some of that $50 savings comes from energy generated directly from the panels during the mid day and not just the batteries. I seriously doubt the batteries (even at the low Costco price) will pay for themselves in the 3+ years owned.

Also since the battery system kept being bolstered by new ones over a period of months it might be hard to get a true cost/kWh on any of them.

I have wondered myself how to factor in the direct power to calculate cents / kWh. But consider this:

$1344 for 36 months
16 x 6 X 207AH x .50 DOD = 9936w = 9.9kW / day
9.9kW * 30 = 298kW / mo
298 * 12 = 3577 kW / year
3577 * 3 = 10731 kW / life
$1344 / 10731 = 12.5 cents / kWh

My calculation of the 1220 cycles to 50% DOD comes out to about 11 cents / kWH.

So, it really comes down to what the utility charges. The OP has grid power and is not producing that much of his total power needs. So if he is in the higher tiers, the reduction could be much more than 11-12 cents / kWH.

But he also said he is draining the batteries down to what appears to be 100%. If that is calculated correctly then he may have sacrificed his batteries, but gotten the cent/ kWH down to 6 cents / kWH and they still have lasted 3 years.

[SunEagle]

I have wondered myself how to factor in the direct power to calculate cents / kWh. But consider this:

$1344 for 36 months
16 x 6 X 207AH x .50 DOD = 9936w = 9.9kW / day
9.9kW * 30 = 298kW / mo
298 * 12 = 3577 kW / year
3577 * 3 = 10731 kW / life
$1344 / 10731 = 12.5 cents / kWh

My calculation of the 1220 cycles to 50% DOD comes out to about 11 cents / kWH.

So, it really comes down to what the utility charges. The OP has grid power and is not producing that much of his total power needs. So if he is in the higher tiers, the reduction could be much more than 11-12 cents / kWH.

But he also said he is draining the batteries down to what appears to be 100%. If that is calculated correctly then he may have sacrificed his batteries, but gotten the cent/ kWH down to 6 cents / kWH and they still have lasted 3 years.

Your math is correct and based on it the cost of 11 cents / kWh is pretty good. But as you indicated, it is still an assumption that you will get 50% DOD for 1220 cycles for each of those batteries. It may be possible for a couple of batteries to last that long but with all of those parallel charging/discharging paths I would think one or more of those batteries will die before getting close to 1220 cycles at 50% DOD.

I would agree that if it was just 2 of those 6v batteries, they could generate 50% DOD in kWh over 1220 cycles which at $85/each would come out to just over $0.11/kWh. But to expand that to 16 would IMO be a stretch.